How to choose the right type of light for your ganja garden.

When growing pot, the more light you have per square foot, the more plant you will get. This is a scientifically proven fact, and it makes sense.

There are four standard lighting options: fluorescent lighting, mercury vapor lighting, metal halide lighting, and high pressure sodium lighting. Each has its own pros and cons based on intensity of light (measured in lumens), heat, and spectrum of color.

Here's an overview of how to choose and use the best method for different stages of growth.

Fluorescent

Fluorescent lighting is a very efficient way to light a large space like an office building. For growing, however, it isn't the best option, as it isn't very intense for the amount of power it sucks up. A fluorescent bulb at 40 watts will only put out about 3,000 lumens. And even with many bulbs in use, fluorescent lighting isn't the right choice for the later stages of growth.

However, for the first stages of growth, – rooting clones or seeds – it is excellent because it is a soft and gentle lighting source that generates very little heat. Clones will thrive under the light of a bank of gentle fluorescent bulbs until the roots take or new growth sprouts from the top of the plant. Then the clones should be put under a more powerful light source.

Keeping clones under fluorescents for too long will cause the plant to become phototropic. A phototropic plant is one that has expended all of its energy in attaining height to reach a weak light source. The space between the leaf branches (the internodal space) will be large, and the plant will be feeble.

Newly rooting clones do not need the same light intensity as plants in the green growth stages. Putting rooting clones under the full radiance of a metal halide will kill them, slowly. The intensity of light and heat will dehydrate the leaves since a clone doesn't have roots to suck up more moisture. This won't be apparent at first because the foliage will actually grow well. What won't grow well, though, is the roots.

Subtle fluorescent lighting is great for clones as the rooting process is dependent on a specific pair of hormones. That is, the levels of each of these hormones determines the speed of root growth. While under intense light, the plant will want to take advantage of this intense level of light and speed up the growth of foliage. Since there's only a finite amount of energy that can be put into growth in total, the hormones that determine the speed of root growth aren't generated in normal amounts. This translates into fairly slow root growth.

While the clone is under intense light, the roots won't grow fast enough to support the plant that is sprouting so much green foliage. The roots cannot keep up, and the plant will eventually starve itself under the nutritional needs of the foliage.

A good level of lighting for rooting clones or seedlings is around 1,500 lumens per square foot of grow space. A fluorescent bulb is about four feet in length and puts out 3,000 lumens. The effective reach of the light is about one foot. So two of these bulbs, totalling 6,000 lumens combined, would be appropriate for a grow area of four square feet.

For more clones, adding pairs of double-bulbed light fixtures will double the clone rooting area as needed.

Mercury vapor

A mercury vapor bulb is stronger than a fluorescent, as a 175-watt bulb will put out 8,000 lumens. However, it is still inappropriate for the later growth stages, as the light isn't strong enough for the large amount of heat the bulb generates. The topmost branches of the plants will get burned being in such close proximity to the bulb.

Unlike fluorescents, mercury vapor bulbs are not suitable for rooting as there is simply too much heat and the light spectrum is a very harsh shade of blue-white. This bulb is cheaper than the other lighting options, but its excessive heat production makes it very impractical. Thus, this lighting option is not recommended.

Metal halide

A metal halide bulb is a good choice for use after clones have taken root, as this bulb puts out tons of light (a 400-watt bulb will create 36,000 lumens) and the heat produced is acceptable. You can hang your bulb to within a foot of the topmost branches and they will not scorch under the heat.

The light has a large amount of blue to it, which is ideal for fast-growing (and smokable) green plants, which need a lot of blue light to grow thick and lush foliage. It's the absolutely perfect spectrum for plants in the main foliage growth stage as this bluish light simulates a summer sun. The foliage growing cycle is simple. If plants are fed regularly and watched for critters and nutrient deficiencies, they'll flourish.

One 1,000-watt metal halide bulb in good working order can service an area of 25 square feet, with a total average light output of 90,000 lumens. This is the optimum level of lighting for plants during the long foliage growth period. Each square foot of growing space should receive a very respectable 3,500 lumens. This will produce huge amounts of healthy green foliage, paving the way for some really killer couch-lock buds later on.

There is no reason to add a second bulb, as buying it, the fixture, the ballast, and electricity is very expensive. Also, a second bulb will produce another source of unwanted heat. Keep in mind also that the power company could notice this addition. A regular on and off increase and decrease of exactly 2,000 watts for months at a time, even in a larger house, won't go unnoticed. You could draw a team of rude visitors.

High pressure sodium

Once plants start flowering, a light source with a more orange spectrum is needed, as it simulates the waning light of the autumn sun, triggering bud production. The high pressure sodium bulb is perfect for this because of its visible orange color. It also puts out 45,000 lumens per 400-watt bulb and creates about the same amount of heat as does the metal halide.

Once the flowering cycle starts, switch to a high pressure sodium bulb. This bulb actually puts out more light than does the metal halide, but in a spectrum that isn't conducive to foliage growth. High pressure sodium is all about the buds: this bulb increases density and potency. Buds will grow fat and healthy, the resin sacs will be full and firm and the foliage will make killer oil or hash after it's harvested.

A 1,000-watt high pressure sodium bulb will put out 112,500 lumens. This amount of light in 25 square feet will work out to 4,500 lumens per square foot. Just think of those fat, juicy buds.

During the flowering/budding stage, overkill is the way to go. As long as the heat is kept under control, more light translates into more buds and more potency. The previous months of growth are all for naught if buds don't turn out very well.

Choose wisely

While having a 1,000-watt bulb is great, not everyone wants to go that far. Perhaps the reason is money, space, or you just don't want that many plants. So feel free to tailor the numbers to fit your situation. There are even smaller bulbs such as the 250-watt, which is good for single or double plant growing, but the most commonly used bulbs start at 400 watts.

That's lighting in a nutshell. Happy growing!